1. Field of the Invention
The field of the invention is that of magnetic reed relay switches.
2. The Prior Art
The magnetic reed relay switch has become well known in the prior art. In its normal configuration the magnetic reed relay switch is a two terminal switch having a normally open configuration. The spring characteristics of the magnetic reed contacts which are usually housed in a non-magnetic closure, such as glass envelope, keep the contacts spread apart. A study state unidirectional magnetic field usually produced by a coil wound around the switch acts to create an attraction between the contacts of the switch. The attraction between the contacts of the switch causes them to close. Contact pressure is increased by the flux increase which is caused by the contacts closing hence, decreasing the reluctance of the circuit. In the normally open configuration, the spring forces of the contacts only need to be enough to overcome any residual magnetic forces due to the retentivity of the magnetic contacts and due to any micro-welding that might occur on contact closure.
To provide a normally closed operation, the switch must be provided in some fashion with another contact. The sensitivity of the switch for a given current handling capability is reduced, since the contact pressure must be obtained entirely from a high spring force which must be overcome by the magnetic field in order to open the contact.
In order to retain the advantage of the normally open configuration, the switch may be biased closed by means of a permanent magnet. An electromagnetic coil may then be used to overcome the permanent magnet bias thereby causing the switch to open. However, if the coil current is increased enough to totally cancel the permanent flux, then increase further, that relay will reclose. The ratio of reclosure to open current is on the order of 2 to 1 with the prior art switch arrangements.